Acoustic wave filter

Abstract

An acoustic wave filter includes at least one serial arm resonance circuit on a path connecting input/output terminals, and at least one parallel arm resonance circuit between a node on the path and a ground, in which each of the at least one serial arm resonance circuit and the at least one parallel arm resonance circuit includes an acoustic wave resonator, a first parallel arm resonance circuit of the at least one parallel arm resonance circuit includes a bridging capacitor connected in parallel to the acoustic wave resonator, an anti-resonant frequency of the first parallel arm resonance circuit is positioned on a higher-frequency side than the pass band, and a resonant frequency of a first serial arm resonance circuit of the at least one serial arm resonance circuit is positioned on a lower-frequency side than the anti-resonant frequency of the first parallel arm resonance circuit.

What is claimed is: 
     
       1. A band pass acoustic wave filter having a pass band and an attenuation band on at least one of a lower-frequency side and a higher-frequency side than the pass band, the acoustic wave filter comprising:
 a first input/output terminal and a second input/output terminal; 
 at least one serial arm resonance circuit on a path connecting the first input/output terminal and the second input/output terminal; and 
 at least one parallel arm resonance circuit between a node on the path and a ground; wherein 
 each of the at least one serial arm resonance circuit and the at least one parallel arm resonance circuit includes at least one acoustic wave resonator; 
 a first parallel arm resonance circuit of the at least one parallel arm resonance circuit includes a bridging capacitor connected in parallel to the at least one acoustic wave resonator; 
 an anti-resonant frequency of the first parallel arm resonance circuit is on the higher-frequency side than the pass band; and 
 a resonant frequency of a first serial arm resonance circuit of the at least one serial arm resonance circuit is on a lower-frequency side than the anti-resonant frequency of the first parallel arm resonance circuit. 
 
     
     
       2. The band pass acoustic wave filter according to  claim 1 , wherein
 any parallel arm resonance circuit of the at least one parallel arm resonance circuit includes
 a respective bridging capacitor connected in parallel to a respective acoustic wave resonator of the at least one acoustic wave resonator; 
 
 an anti-resonant frequency of any parallel arm resonance circuit of the at least one parallel arm resonance circuit is on the higher-frequency side than the pass band; and 
 the resonant frequency of the first serial arm resonance circuit is on a lower-frequency side than the anti-resonant frequency of any parallel arm resonance circuit of the at least one parallel arm resonance circuit. 
 
     
     
       3. A band pass acoustic wave filter having a pass band and an attenuation band on at least one of a lower-frequency side and a higher-frequency side than the pass band, the acoustic wave filter comprising:
 a first input/output terminal and a second input/output terminal; 
 at least one serial arm resonance circuit on a path connecting the first input/output terminal and the second input/output terminal; and 
 at least one parallel arm resonance circuit between a respective node on the path and a ground; wherein 
 any serial arm resonance circuit of the at least one serial arm resonance circuit includes a serial arm resonator on the path; 
 any parallel arm resonance circuit of the at least one parallel arm resonance circuit includes a parallel arm resonator between the respective node and the ground; 
 each of the at least one serial arm resonator and the at least one parallel arm resonator includes at least one acoustic wave resonator including an IDT (InterDigital Transducer) electrode provided on a substrate having piezoelectricity; 
 the IDT electrode includes a pair of comb-shaped electrodes each including a plurality of electrode fingers extending in a direction intersecting with an acoustic wave propagation direction and in parallel or substantially in parallel to one another, and bulbar electrodes connecting ends of electrode fingers of the plurality of electrode fingers to each other; 
 where, among the plurality of electrode fingers:
 a first electrode finger which is not connected to the busbar electrodes is defined as a first withdrawal electrode, 
 a second electrode finger having a maximum electrode finger width, and including an electrode finger width two or more times an average electrode finger width of the plurality of electrode fingers excluding the second electrode finger is defined as a second withdrawal electrode, and 
 a third electrode finger connected to a same one of the busbar electrodes as adjacent electrode fingers on both adjacent sides of the third electrode finger in the acoustic wave propagation direction is defined as a third withdrawal electrode; 
 
 a parallel arm resonator included in a first parallel arm resonance circuit of the at least one parallel arm resonance circuit includes at least one of the first withdrawal electrode, the second withdrawal electrode, and the third withdrawal electrode; 
 an anti-resonant frequency of the first parallel arm resonance circuit is on the higher-frequency side than the pass band; and 
 a resonant frequency of a first serial arm resonance circuit of the at least one serial arm resonance circuit is on a lower-frequency side than the anti-resonant frequency of the first parallel arm resonance circuit. 
 
     
     
       4. The band pass acoustic wave filter according to  claim 3 , wherein the parallel arm resonator included in the first parallel arm resonance circuit of the at least one parallel arm resonance circuit includes the first withdrawal electrode. 
     
     
       5. The band pass acoustic wave filter according to  claim 3 , wherein
 a parallel arm resonator included in any parallel arm resonance circuit of the at least one parallel arm resonance circuit includes the first withdrawal electrode or the second withdrawal electrode; 
 an anti-resonant frequency of any parallel arm resonance circuit is on the higher-frequency side than the pass band; and 
 the resonant frequency of the first serial arm resonance circuit is on a lower-frequency side than an anti-resonant frequency of any parallel arm resonance circuit. 
 
     
     
       6. The band pass acoustic wave filter according to  claim 1 , wherein a resonant frequency of the first parallel arm resonance circuit is on the lower-frequency side than the pass band, and the resonant frequency of the first parallel arm resonance circuit of a resonant frequency of the at least one parallel arm resonance circuit is closest to a low frequency end portion of the pass band. 
     
     
       7. The band pass acoustic wave filter according to  claim 1 , wherein
 a resonant frequency of a second serial arm resonance circuit of the at least one serial arm resonance circuit is on the higher-frequency side than the pass band; and 
 an impedance of the second serial arm resonance circuit in the pass band is capacitive. 
 
     
     
       8. The band pass acoustic wave filter according to  claim 1 , wherein
 a third serial arm resonance circuit of the at least one serial arm resonance circuit includes:
 an acoustic wave resonator of the at least one acoustic wave resonator; and 
 a bridging capacitor connected in parallel to the acoustic wave resonator; 
 
 a resonant frequency of the third serial arm resonance circuit is on the lower-frequency side than the pass band; and 
 an anti-resonant frequency of the third serial arm resonance circuit is on the higher-frequency side than the pass band. 
 
     
     
       9. The band pass acoustic wave filter according to  claim 8 , wherein
 the acoustic wave resonator of the third serial arm resonance circuit includes an IDT electrode provided on a substrate having piezoelectricity; 
 the IDT electrode includes a pair of comb-shaped electrodes each including a plurality of electrode fingers extending in a direction intersecting with an acoustic wave propagation direction and in parallel or substantially in parallel to one another, and busbar electrodes connecting ends of electrode fingers of the plurality of electrode fingers to each other; 
 where, among the plurality of electrode fingers:
 a first electrode finger which is not connected to the busbar electrodes is defined as a first withdrawal electrode, 
 a second electrode finger having a maximum electrode finger width, and having an electrode finger width two or more times an average electrode finger width of the plurality of electrode fingers excluding the second electrode finger is defined as a second withdrawal electrode, and 
 a third electrode finger connected to a same one of the busbar electrodes as adjacent electrode fingers on both adjacent sides in the acoustic wave propagation direction is defined as a third withdrawal electrode; 
 
 the third serial arm resonance circuit includes any of the first withdrawal electrode, the second withdrawal electrode, and the third withdrawal electrode; 
 a resonant frequency of the third serial arm resonance circuit is on the lower-frequency side than the pass band; and 
 an anti-resonant frequency of the third serial arm resonance circuit is on the higher-frequency side than the pass band. 
 
     
     
       10. The band pass acoustic wave filter according to  claim 3 , wherein
 a resonant frequency of the first parallel arm resonance circuit is on the lower-frequency side than the pass band; and 
 the resonant frequency of the first parallel arm resonance circuit of a resonant frequency of the at least one parallel arm resonance circuit is closest to a low frequency end portion of the pass band. 
 
     
     
       11. The band pass acoustic wave filter according to  claim 3 , wherein
 a resonant frequency of a second serial arm resonance circuit of the at least one serial arm resonance circuit is on the higher-frequency side than the pass band; and 
 an impedance of the second serial arm resonance circuit in the pass band is capacitive. 
 
     
     
       12. The band pass acoustic wave filter according to  claim 3 , wherein
 a third serial arm resonance circuit of the at least one serial arm resonance circuit includes:
 an acoustic wave resonator of the at least one acoustic wave resonator; and 
 a bridging capacitor connected in parallel to the acoustic wave resonator; 
 
 a resonant frequency of the third serial arm resonance circuit is on the lower-frequency side than the pass band; and 
 an anti-resonant frequency of the third serial arm resonance circuit is on the higher-frequency side than the pass band. 
 
     
     
       13. The band pass acoustic wave filter according to  claim 12 , wherein
 the acoustic wave resonator of the third serial arm resonance circuit includes an IDT electrode provided on a substrate having piezoelectricity; 
 the IDT electrode includes a pair of comb-shaped electrodes each including a plurality of electrode fingers extending in a direction intersecting with an acoustic wave propagation direction and in parallel or substantially in parallel to one another, and busbar electrodes connecting ends of electrode fingers of the plurality of electrode fingers to each other; 
 where, among the plurality of electrode fingers:
 a first electrode finger which is connected to neither of the busbar electrodes of the pair of comb-shaped electrodes is defined as a first withdrawal electrode, 
 a second electrode finger having a maximum electrode finger width, and having an electrode finger width two or more times an average electrode finger width of the plurality of electrode fingers excluding the second electrode finger is defined as a second withdrawal electrode, and 
 a third electrode finger connected to a same one of the busbar electrodes as adjacent electrode fingers on both adjacent sides in the acoustic wave propagation direction is defined as a third withdrawal electrode; 
 
 the third serial arm resonance circuit includes any of the first withdrawal electrode, the second withdrawal electrode, and the third withdrawal electrode; 
 a resonant frequency of the third serial arm resonance circuit is on the lower-frequency side than the pass band; and 
 an anti-resonant frequency of the third serial arm resonance circuit is positioned on the higher-frequency side than the pass band. 
 
     
     
       14. The band pass acoustic wave filter according to  claim 1 , wherein
 the at least one serial arm resonance circuit includes four series arm resonators; and 
 the at least one parallel arm resonance circuit includes three parallel arm resonators. 
 
     
     
       15. The band pass acoustic wave filter according to  claim 3 , wherein
 the at least one serial arm resonance circuit includes four series arm resonators; and 
 the at least one parallel arm resonance circuit includes three parallel arm resonators. 
 
     
     
       16. The band pass acoustic wave filter according to  claim 1 , wherein the bridging capacitor includes a pair of comb-shaped electrodes. 
     
     
       17. The band pass acoustic wave filter according to  claim 3 , wherein the bridging capacitor includes a pair of comb-shaped electrodes. 
     
     
       18. The band pass acoustic wave filter according to  claim 1 , wherein the bridging capacitor is a chip capacitor. 
     
     
       19. The band pass acoustic wave filter according to  claim 3 , wherein the bridging capacitor is a chip capacitor.